1. Field of the Invention
The present invention relates generally to an apparatus and method for providing Voice over Internet Protocol (VoIP) service based on an IP multimedia subsystem (IMS), and in particular, to an apparatus and method for providing VoIP service based on an IP multimedia subsystem in an integrated environment of an Institute of Electrical and Electronics Engineers (IEEE) 802.16 system and a cordless phone or Digital European Cordless Telecommunications (DECT). The Institute of Electrical and Electronics Engineers (IEEE) 802.16 system is a broadband wireless communication system.
2. Description of the Related Art
An existing converged voice service (called one phone service) between heterogeneous networks is provided using a cordless phone/cellular structure and a Bluetooth/cellular structure.
These structures provide a terminal with a Public Switched Telephone Network (PSTN) based voice service in a range where the cordless phone is usable, and a Mobile Switching Center (MSC) based voice service in the cellular network. The existing converged voice service between the heterogeneous networks is a circuit switched based service and provides call originating/terminating services over two telephone numbers, which are allocated to the PSTN and the cellular network, respectively. Because the service is provided over the different networks, there are many problems in terms of charging and service delivery between the different service providers.